While writing the partial journal entries we assumed that the page
associated with the journal would always in locatable. This incorrect
assumption resulted in the following BUG

kernel BUG at /home/benixon/WD_SMR/kernels/linux-3.3.7-logfs/fs/logfs/journal.c:569!
EIP is at logfs_write_area+0xb6/0x109 [logfs]
EAX: 00000000 EBX: 00000000 ECX: ef6efea4 EDX: 00000000
ESI: 001b9000 EDI: f009e000 EBP: c3c13f14 ESP: c3c13ef0
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process sync (pid: 1799, ti=c3c12000 task=f07825b0 task.ti=c3c12000)
Stack:
01001000 c3c13f26 781b9000 00000000 f009e000 f7286000 f1f83400 f8445071
f1f83400 c3c13f30 f8445ae9 c3c13f20 0000100a 000ee000 f009e000 00000001
c3c13f5c f8445d17 c05eb0ee 00000000 f1f83400 ef718000 f009e25c ea9c3d80
Call Trace:
[<f8445071>] ? account_shadow+0x16d/0x16d [logfs]
[<f8445ae9>] logfs_write_je+0x2a/0x44 [logfs]
[<f8445d17>] logfs_write_anchor+0x114/0x228 [logfs]
[<c05eb0ee>] ? empty+0x5/0x5
[<f8444522>] logfs_sync_fs+0x1e/0x31 [logfs]
[<c051be66>] __sync_filesystem+0x5d/0x6f
[<c051be8d>] sync_one_sb+0x15/0x17
[<c04ff8b0>] iterate_supers+0x59/0x9a
[<c051be78>] ? __sync_filesystem+0x6f/0x6f
[<c051befc>] sys_sync+0x29/0x4f
[<c084285f>] sysenter_do_call+0x12/0x28
EIP: [<f8445127>] logfs_write_area+0xb6/0x109 [logfs] SS:ESP 0068:c3c13ef0
---[ end trace ef6e9ef52601a945 ]---

The fix is to create the pagecache page if it is not locatable.

Reported-and-tested-by: Benixon Dhas <Benixon.Dhas@wdc.com>
Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>